This invention relates to a catalyst system suitable for the conversion of synthesis gas to hydrocarbons, more particularly to a catalyst system comprising a copper-containing component together with an iron-containing component and a wax cracking component such as a Zeolite. This invention also relates to a process for the conversion of synthesis gas to hydrocarbons using the above-described catalyst system.
The conversion of synthesis gas to hydrocarbons by the Fischer-Tropsch process is well known. Usually the catalyst employed in the Fischer-Tropsch process is an iron oxide-containing material although other metal oxides such as those of cobalt, nickel, ruthenium, thorium, rhodium and osmium have been described. However, it is a feature of known Fischer-Tropsch catalysts that a significant proportion of the hydrocarbon product is either in the form of methane and/or wax and this is a disadvantage because the need at the present time is for liquid hydrocarbons suitable for use as transportation fuels.
To reduce the wax content of the product it has been previously proposed to either incorporate with the Fischer-Tropsch catalyst a cracking component such as a Zeolite or to pass the product from the Fischer-Tropsch catalyst over a cracking catalyst in a separate stage.
For example, U.S. Pat. Nos. 4,046,830 and 4,279,830 describe the conversion of synthesis gas to oxygenates and hydrocarbons by first contacting the synthesis gas with a Fischer-Tropsch catalyst in a first stage and then passing the product from the first stage over an acidic crystalline Zeolite in a second stage. The process is operated as two stages because the conditions under which the cracking catalyst is operated are more severe than those required for the hydrocarbon synthesis. It would be an advantage to be able to operate both reactions in a single stage since this would eliminate a reactor vessel and it is an object of the present invention to provide such a process.
U.S. Pat. No. 4,086,262 discloses a process for the conversion of synthesis gas using a single stage process wherein the catalyst is a mixture of (i) a carbon monoxide reducing catalyst such as a methanol catalyst or an iron-containing Fischer-Tropsch catalyst and (ii) a ZSM-5 type Zeolite. However, the products described in this patent contain significant amounts of gaseous hydrocarbons, particularly methane which in all cases exceeds 10 percent by weight of the hydrocarbon product.
It is therefore an object of the present invention to provide a single stage process for the conversion of synthesis gas to hydrocarbons and thereby avoid the disadvantage of the two stages described in U.S. Pat. Nos. 4,046,830 and 4,279,830 and at the same time to produce a hydrocarbon product that either contains less than 10 percent by weight of methane or contains at least 70 percent by weight of hydrocarbons in the range C.sub.3 to a boiling point of 340.degree. C.